Assessment of the effect of Piriformospora indica symbiosis and paclobutrazol application on growth parameters in sweet basil (Ocimum basilicum L.) in response to salinity stress

water and soil salinity are the serious and growing problem in the world, a large part of our country is also faced with this problem. Nowadays, application of symbiont microorganisms such as mycorrhiza-like fungi, P. indica, is one of the strategies using for improvement of growth and yield in unpleasant environmental conditions such as water and soil salinity. But beside the application of these microorganisms, today the use of materials such as paclobutrazol has also increased, which has the ability to regulate the growth and decrease the negative effects of environmental stresses. The aim of this study is to investigate the effect of these factors on the properties of Basil in saline condition as well as compare the efficiency of them.
The study was conducted based on randomized complete block design with three replications at Sari Agricultural Sciences and Natural Resources University in 2015. Treatments included two levels of coexistence (control and inoculated with the fungus), three levels of paclobutrazol (0, 20 and 40 mg.L-1) and four salinity levels (0, 3, 6 and 9 dS.m-1 NaCl). We study leaf, aerial parts and root fresh and dry weight, height, number of leaves, leaf area, root length, leaf relative water content, leaf chlorophyll content, essential oil content and essential oil yield, lipids peroxidation and hydrogen peroxide content, antioxidant enzymes activity including superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX).
The findings of this study indicate that inoculation significantly increased leaf, aerial parts and root fresh and dry weight in stress condition. Paclobutrazol application although reduced leaf and plant fresh and dry weight in normal condition, it could improve them in stress condition. Symbiosis also considerably increased height, number of leaves, leaf area, root length, leaf relative water content, leaf chlorophyll content, and essential oil content of basil in saline condition, as the most positive effects of fungi was observed at medium and high salinity levels. However, in similar situation paclobutrazol foliar spray had significant effect on only leaf area, root length, leaf relative water content, leaf chlorophyll content and essential oil yield. P. indica symbiosis and paclobutrazol application also redused membrane lipid peroxidation as a result of stress. However, the decrease in fungal treatments was more notable than paclobutrazol treatments. Inoculation and paclobutrazol treatments also increased considerably the content of hydrogen peroxide and superoxide dismutase, catalase and ascorbate peroxidase activity under stress.
It seems that, symbiotic relationship of basil with fungi P. indica can improve basil growth properties by increase salt tolerance in such condition. Paclobutrazol application is also effective in mitigating the adverse effects of stress, although not as powerful as fungi inoculation.